Cleaning of wellbores



United States Patent 3,241,614 CLEANING 9F WELLBGRES Theodore A. Bertness, Whittier, Calif, assignor to Socony Mobil Oil Company, Inc, a corporation of New York No Drawing. Filed .Fuly 8, 1963, Sex. No. 293,259 12 Claims. (Cl. 166-41) This application is a continuation-in-part of my copending application Serial No. 99,059, filed March 29, 1961, and now abandoned.

This invention relates to cleaning of Wellbores and relates more particularly to cleaning of wellbores to remove therefrom deposits of paraffin and other high-viscosity hydrocarbons.

In the production of petroleum oil or gas from a subterranean formation through a wellbore leading the surface of the earth, difiiculty is often encountered by reason of accumulation within the wellbore of heavy hydrocarbons. As a result of lowering of temperature and other factors, heavy hydrocarbons, such as parafiins and tars, accumulate within the wellbore, with consequent plugging of the wellbore. For example, paraffins and tars accumulate within a wellbore at the perforations of the liner, at tubing perforations, and within the tubing. They also accumulate within pumps, on sucker rods, and else- Where. These accumulations of heavy hydrocarbons are solid or semisolid at the conditions existing within the wellbore and reduce the size of the passageways within the wellbore. As a result, fluid flow, either of liquid or gas, through the passageways becomes restricted. In aggravated cases, accumulation of these heavy hydrocarbons can occur to the extent that fluid flow through the wellbore is completely restricted.

Attempts have been made to remove the accumulations of these heavy hydrocarbons by procedures involving contacting the accumulations with a solvent for heavy hydrocarbons. The purpose of these procedures is to dissolve the accumulations whereby they may be readily washed out of the wellbore. However, these atttempts are usually unsuccessful. Apparently, the accumulations constitute a mass of heavy hydrocarbons emulsified with the water that is produced along with the petroleum oil or gas. The emulsified water within the mass of heavy hydrocarbons effectively retards the action of the solvents in dissolving the heavy hydrocarbons. Additionally, the accumulations are apparently covered on their outer surfaces with a thin film of the produced water which further retards the action of the solvents in dissolving the heavy hydrocarbons.

It is an object of this invention to clean a wellbore. It is another object of this invention to remove accumulations of heavy hydrocarbons from a wellbore. It is another object of this invention to increase the rate of production of petroleum from a wellbore. It is another object of this invention to prevent the formation of accumulations of heavy hydrocarbons within a wellbore. These and other objects of the invention will become apparent from the following detailed description.

In accordance with the invention, a wellbore is treated by a procedure involving the steps of contacting a solid or semisolid accumulation of hydrocarbons within the wellbore with a liquid mixture comprising a solvent for hydrocarbons and a surfactant, and thereafter contacting the hydrocarbon accumulation with water.

I have discovered that by contacting a hydrocarbon accumulation within a wellbore with a liquid mixture comprising a solvent for hydrocarbons and a surfactant, the hydrocarbon accumulations are apparently softened. The mixture of the solvent for hydrocarbons and the surfactant, acting together, are able to displace any film of water on the outer surface of the accumulation. Further, the mixture of the solvent for hydrocarbons and the surfactant,

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acting together, are able to penetrate the mass of heavy hydrocarbons emulsified with Water. However, because of the presence of the emulsified water, penetration of the accumulation by the solvent for hydrocarbons does not result in solution of the hydrocarbons. Rather, penetration of the accumulation by the solvent for hydrocarbons results only in a preconditioning of the accumulation for the action of the water. Upon contact of the accumulation with the water in the second step of the process, the heavy hydrocarbons become dispersed in the water. The accumulation thus becomes displaced from its position within the wellbore and its action in restricting fluid flow through the passageways within the wellbore is eliminated. Upon subsequent movement of the water out of the wellbore, the dispersed heavy hydrocarbons accompany the water and are removed from the wellbore.

Various types of solvent for hydrocarbons may be employed in the first step of the procedure. The solvents may be liquid hydrocarbons, liquid halogenated hydrocarbons, liquid amine substituted hydrocarbons, and liquid oxygenated hydrocarbons, including alcohols, ketones, and acids. The liquid hydrocarbons may be aliphatic or aromatic hydrocarbons. Included among the solvents are petroleum fractions such as kerosene, or fractions similar to kerosene, such as purified kerosene fractions, and gasoline. Also included among these solvents are benzene, xylene, toluene, n-pentane, n-heptane, chlorohexylamine, propylene diamine, ethylene diamine, diethylene triamine, methylene chloride, perchloro ethylene, carbon tetrachloride, trichloroethane, dioxane, methylethyl ketone, acetic acid, carbon disulfide, and the cresylic acids. Of the solvents for hydrocarbons, it is preferred to employ toluene, xylene, or benzene. It is not necessary that only one solvent be employed. For example, a mixture of two or more solvents may be employed. Additionally, if desired or necessary, a corrosion inhibitor may be added to the solvent.

The surfactant for use with the solvent for hydrocarbons in the first step of the procedure may be any type of compound possessing surface-active properties and solubility in both oil and water. These surfactants may be regarded as compounds which possess a water-soluble portion and an oil-soluble portion. Thus, the surfactants are capable of dissolving to some extent in either water or in oil. Depending upon the hydrophilic properties of the Water-soluble portion of the compound and lyophilic properties of the oil-soluble portion of the compound, the compound may be more soluble in water than in oil or more soluble in oil than in water. Preferably, the surfactant to be employed should have a greater degree of water solubility than oil solubility. Further, it is preferred that the surfactant be nonionic.

Of the surfactants that may be employed in the first step of the procedure, it is preferred to employ an oxyethylene ether of an alkyl aryl compound. The alkyl aryl portion of the surfactant, i.e., the lyophilic portion, may contain from 9 to 18 carbon atoms. The oxyethylene portion of the compound, i.e., the hydrophilic portion, may contain between 20 and 50 mols of ethylene oxide. Particularly effective results have been obtained employing oxyethylene ether of nonylphenol where the oxyethylene chain contains on the average 30 mols of ethylene oxide.

The liquid mixture comprising the solvent for hydrocarbon and the surfactant should contain the surfactant in an amount at least as great as 0.1 percent by weight of the mixture. Preferably, however, greater amounts should be employed. For example, an amount of surfactant of 5 percent by weight of the mixture has been found to be satisfactory. An amount of surfactant as great as 10 percent by weight of the mixture can also be employed.

The amount of liquid mixture comprising the solvent for hydrocarbon and the surfactant to be employed will vary depending upon the amount of accumulation of heavy hydrocarbon to be displaced. Ordinarily, a determination as to the amount of accumulation of heavy hydrocarbon is difficult to make. However, where the amount of accumulation of heavy hydrocarbon is known, the amount of liquid mixture to be employed should be equal to at least one-half the volume of the accumulation of heavy hydrocarbon. Greater amounts, for example, up to a volume equal to that of the accumulation of heavy hydrocarbon may be employed. To be assured of adequate treatment of the wellbore, a volume of liquid mixture equal to the volume of the passageways within the wellbore containing accumulations of heavy hydrocarbon to be removed is employed. Additionally, the step of contacting the accumulation of heavy hydrocarbon with the liquid mixture can be repeated, if desired. This step can be repeated once or more than once.

In the second step of the procedure, the hydrocarbon accumulation within the wellbore is contacted with water. Contact of the accumulation with Water effects an emulsification of the heavy hydrocarbons with the water. Displacement of the accumulations and emulsification of the hydrocarbons with the water is assisted by agitation of the Water. This agitation may be obtained by flowing the water through the wellbore at the location of the hydrocarbon accumulation. Additionally, agitation may be effected, where an otherwise quiescent body of water is in contact with the accumulation, by passing a gas through the body of water to effect a frothing or bubbling action. Other means of effecting agitation of the water in contact with the accumulation may be employed.

The amount of water employed in the second step of the procedure may be the same as that of the liquid mixture of the solvent for hydrocarbons and the surfactant employed in the first step of the procedure. However, it is preferred to employ larger volumes of water. For example, it is preferred that the volume of water employed be between three and five times the volume of liquid mixture of the solvent for hydrocarbons and the surfactant employed. However, if desired, a still greater volume may be employed. Thus, for example, the volume of water can be ten or more times the volume of the liquid mixture of the solvent for hydrocarbons and the surfactant.

In accordance with a particular feature of the invention, the water employed in the second step of the procedure is in admixture with a surfactant. Whereas contact of the hydrocarbon accumulation with water subsequent to the mixture of solvent for hydrocarbon and surfactant results in displacement and emulsification of the heavy hydrocarbons, a more rapid and more effective displacement and emulsification occurs where the water contains a surfactant. The surfactants employed in admixture with the water in the second step of the procedure may be the same surfactants employed in admixture with the solvent for hydrocarbons in the first step of the procedure. Preferably, the surfactant employed in admixture with the water in the second step of the process is oxyethylene ether of nonylphenol where the oxyethylene chain contains on the average 30 mols of ethylene oxide.

Where a surfactant is employed in admixture with the water in the second step of the process, the amount of the surfactant with respect to the amount of water should be at least 0.1 percent by weight. However, a larger amount, for example percent by weight, may be employed. If desired, larger amounts, up to percent by weight, of the mixture can also be employed.

If desired, the step of contacting the accumulation of heavy hydrocarbon with water can be repeated. This step can be repeated once or more than once. As stated above, the step of contacting the accumulation of heavy hydrocarbon with the liquid mixture of the solvent for hydrocarbons and the surfactant may be repeated once or more than once. In this connection, following each step of contacting the accumulation of heavy hydrocarbon with the liquid mixture, the second step of the procedure of contacting the accumulation with water can be carried out one or more times. Alternatively, the step or" contacting the accumulation with water, whether carried out one or more times, can be postponed until after the step of contacting the accumulation with the liquid mixture has been carried out two or more times. If desired, the steps of contacting the accumulation with liquid mixture of the solvent for hydrocarbon and surfactant and with water can be alternated.

Following contact of the hydrocarbon accumulation with the mixture of solvent for hydrocarbons and the surfactant and contact with the water, the accumulations will have become displaced from their position within the wellbore. Production of fluid, either liquid or gas, from the producing formation of the earth to the wellbore can result in removal of the emulsified accumulation. However, if desired or necessary, a fiuid may be passed into the wellbore to remove the hydrocarbon accumulation emulsified in the water. For example, a gas may be injected into the wellbore to effect the formation of a froth and to remove the froth from the wellbore. Other methods may be used for removing from the wellbore the water containing the emulsified hydrocarbon accumulation.

As stated, the second step of the procedure involves contact of the accumulation of heavy hydrocarbon with water. The water employed for this purpose is injected into the wellbore to contact the accumulation. On the other hand, water is often produced into the wellbore along with the gas or oil from a producing earth formation. In these cases, part or all of the water for the second step of the procedure can be obtained by producing water into the wellbore from an earth formation. Where water in admixture with surfactant is desired for use in the second step, the surfactant, in mixture with a liquid if desired, is injected into the wellbore and mixed with the produced water. However, to insure contact of the accumulation with water, i.e., to carry out the second step of the procedure, water should be injected into the wellbore, regardless of producing water from an earth formation into the wellbore.

In many instances, following removal of accumulation of heavy hydrocarbons, the conditions resulting in the accumulation of the heavy hydrocarbons within the wellbore will persist. Thus, following removal of a hydrocarbon accumulation from the wellbore, further accumulation can take place. I have found that further accumulation of heavy hydrocarbon may be prevented by periodic treatment of the wellbore with a mixture of solvent for hydrocarbon and surfactant. The solvents for hydrocarbons and surfactants may be those previously described. In preventing later accumulation of heavy hydrocarbons, the mixture of solvent for hydrocarbon and surfactant is injected into the wellbore and passed through the passageways where accumulation of heavy hydrocarbon would occur. Thus, the mixture may be injected at the bottom of the well through tubing so that it may pass through the well along with the produced fluid. The intervals at which this treatment may be carried out may be daily or be less often. Apparently, contact of the passageways within the wellbore with the mixture of solvent for hydrocarbon and surfactant maintains a water-wet surface within the passageways through which the fluid flows. These water-wet surfaces repel the deposition of heavy hydrocarbons and thus the accumulation of these heavy hydrocarbons is prevented.

In preventing accumulation of heavy hydrocarbons, the liquid mixture of solvent for hydrocarbon and surfactant and the water can be combined. Thus, there can be injected into the wellbore a mixture of solvent, surfactant, and water. The relative amounts of solvent for hydrocarbon and surfactant may be as described above. However, greater amounts of surfactant relative to the solvent for hydrocarbon may be employed. Thus, for example, the amount of surfactant may be as high as 65 percent by weight of the solvent or of the solvent and water where a mixture is employed. The water in the mixture of solvent, surfactant, and water may be in an amount as high as 75 percent by volume of the solvent and water.

The following examples will be further illustrative of the invention.

Example I The rate of production from a gas well was continually decreasing as the result of accumulation of wax within the tubing of the well. Eventually, the well reached a rate of production of 220,000 cubic feet of gas per day. At this time, the well was shut down. One barrel of a liquid mixture of toluene and polyoxyethylene ether of nonylphenol having an average of 30 mols of ethylene oxide in the oxyethylene chain was lubricated into the well through the tubing. The polyoxyethylene ether of nonylphenol constituted 5 percent by weight of the liquid mixture. The well was then shut in for a period of eight hours. Thereafter, a low rate of production of gas from the well was started in order to create agitation of the liquid mixture. After about one hour of this agitation, the well was again shut in. Two barrels of water containing polyoxyethylene ether of nonylphenol having an average of 30 mols of ethylene oxide in the oxyethylene chain were then lubricated down the casing to contact the wax accumulation previously contacted by the liquid mixture of toluene and surfactant. The water contained 5 percent by weight of the ether. A low rate of production of gas was carried out for about one-half hour to agitate the mixture of water and surfactant in contact with the wax. Thereafter, full production through the tubing was effected to blow down the well. As a result of this blowdown, the well produced a foamy liquid comprising solvent and surfactant, water and surfactant, and emulsified wax.

The steps of lubricating down the tubing one barrel of liquid mixture of solvent for hydrocarbons and the surfactant agitating by slow production of gas, and lubricating down the casing two barrels of water and the surfactant, agitating by slow production of gas, and blowdown from the tubing was repeated twice. At each blowdown, there was produced a foamy liquid comprising the solvent and surfactant, water and surfactant, and emulsified wax. At the third blowdown, however, the amount of emulsified wax in the liquid was considerably smaller than in the liquid produced by the first and second blowdowns. Following the third blowdown, the well was put on production and produced gas at a rate of 520,000 cubic feet per day, which rate was more than twice the rate at which the well was producing prior to removal of the accumulation of wax.

Example [I A gas Well was producing 25,000 cubic feet of gas per day. However, the potential of this well was higher than this figure and the low rate of production was due to accumulation of tar within the well. The well was treated, in a first step, by lubricating down the tubing one barrel of liquid mixture of toluene and polyoxyethylene ether of nonylphenol where the ether contained an average of 30 mols of ethylene oxide in the oxyethylene chain. The ether was in the amount of 5 percent by weight of the liquid mixture. After about one-half hour of contact of the liquid mixture with the accumulation of tar, two barrels of water containing 5 percent by weight of polyoxyethylene ether of nonylphenol were lubricated down the tubing. This ether also contained an average of 30 mols of ethylene oxide in the oxyethylene chain. The well was blown down one-half hour later to remove the mixture of toluene and surfactant, water and surfactant, and emulsified tar. The same procedure was repeated. At blowdown, following this repetition of the procedure, the liquid produced from the well contained but little 6 emulsified tar. The well was then placed on production and the rate of production was 2 million cubic feet of gas per day.

The well maintained the rate of production of gas of 2 million cubic feet per day for a short time and then gradually dropped to 400,000 cubic feet of gas per day, indicating accumulation of tar within the well. Upon attaining this latter rate of production, there was injected daily into the well through the annulus between the tubing and the casing one quart of a liquid mixture consisting of 61.5 weight percent of polyoxyethylene ether of nonylphenol containing an average of 30 mols of ethylene oxide in the oxyethylene chain, 10 weight percent of methanol, and 28.5 weight percent of water. The rate of production increased to 800,000 cubic feet per day and continued at this rate of production with daily injection of the liquid mixture. The well was subsequently shut down for a period of approximately one month. On the well being placed back on production, the daily treatment was changed to injection into the wellbore of five gallons of a mixture having the following composition: 32 gallons of an aromatic oil obtained by sulfur dioxide extraction of kerosene, 2 gallons of isopropyl alcohol, 0.1 gallon of water, and 1.1 pounds of polyoxyethylene ether of nonylphenol containing an average of 30 mols of ethylene oxide in the oxyethylene chain. This mixture was prepared to have a cloud point of approximately --20 F. so that it could be handled satisfactorily during winter months. Average production from the Well under this treatment was at a level of about 1,200,000 cubic feet per day.

Having thus described my invention, it will be understood that such description has been given by way of illustration and example and not by way of limitation, reference for the latter purpose being had to the appended claims.

What is claimed is:

l. A process for treating a wellbore containing an accumulation of heavy hydrocarbon to clean. said wellbore of said accumulation which comprises contacting at least once in an essentially static manner for at least 0.5 hour said accumulation comprising heavy hydrocarbon and water with a liquid mixture consisting essentially of solvent for hydrocarbons and lyophilic-hydrophilic surfactant consisting essentially of an oxyethylene ether of an alkyl aryl compound in which the lyophilic portion has 9 to 18 carbon atoms and the hydrophilic portion has between 20 and 50 mols of ethylene oxide, said liquid mixture being capable of penetrating and softening the aforesaid accumulation of heavy hydrocarbon and water to precondition the aforesaid accumulation of heavy hydrocarbon and water to ensure dispersion of said heavy hydrocarbon in Water, thereafter at least once contacting said preconditioned accumulation of heavy hydrocarbon and water with a volume of extraneous Water at least equal to the volume of the aforesaid liquid mixture and dispersing said preconditioned accumulation of heavy hydrocarbon in said extraneous water.

2. A process for treating a wellbore containing an accumulation of heavy hydrocarbon to clear said wellbore of said accumulation which comprises contacting at least once in an essentially static manner for at least 0.5 hour said accumulation comprising heavy hydrocarbon and Water with a first liquid mixture consisting essentially of solvent for hydrocarbons and lyophilic-hyrlrophilic surfactant consisting essentially of an oxyethylene ether of an alkyl aryl compound in which the lyophilic portion has 9 to 18 carbon atoms and the hydrophilic portion has between 20 and 50 mols of ethylene oxide, said first liquid mixture being capable of penetrating and softening the aforesaid accumulation of heavy hydrocarbon and water to precondition the aforesaid accumulation of heavy hydrocarbon and water to ensure dispersion of said heavy hydrocarbon in water, thereafter at least once contacting said preconditioned accumulation of heavy hydrocarbon and water with a volume of a second liquid mixture comprising extraneous water and surfactant at least equal to the volume of the first liquid mixture and dispersing said accumulation of heavy hydrocarbon in said second liquid mixture.

3. A process for treating a wellbore containing an accumulation of heavy hydrocarbon to clear said wellbore of said accumulation which comprises contacting at least once in an essentially static manner for at least 0.5 hour said accumulation comprising heavy hydrocarbon and Water with a first liquid mixture consisting essentially of solvent for hydrocarbons and lyophilic-hydrophilic surfactant consisting essentially of an oxyethylene ether of an alkyl aryl compound in which the lyophilic portion has 9 to 18 carbon atoms and the hydrophilic portion has between 20 and 50 mols of ethylene oxide, said first liquid mixture being capable of penetrating and softening the aforesaid accumulation of heavy hydrocarbon and water to precondition the aforesaid accumulation of heavy hydrocarbon and water to ensure dispersion of said heavy hydrocarbon in water, agitating said first liquid mixture in contact with the aforesaid accumulation of heavy hydrocarbon and water, thereafter at least once contacting said preconditioned accumulation of heavy hydrocarbon and water with a volume of a second liquid mixture comprising extraneous water and surfactant at least equal to the volume of said first liquid mixture, agitating said second liquid mixture in contact with said preconditioned accumulation of heavy hydrocarbon and water and dispersing said accumulation of heavy hydrocarbon in said second liquid mixture.

4. A process for treating a wellbore containing an accumulation of heavy hydrocarbon within passageways in said wellbore to clean said passageways of said accumulation comprising the steps of (l) contacting at least once in an essentially static manner for at least 0.5 hour said accumulation with a liquid mixture consisting essentially of solvent for hydrocarbons and lyophilic-hydrophilic surfactant consisting essentially of an oxyethylene ether of an alkyl aryl compound in which the lyophilic portion has 9 to 18 carbon atoms and the hydrophilic portion has between 20 and 50 mols of ethylene oxide, said liquid mixture being capable of penetrating and softening the aforesaid accumulation to precondition the aforesaid accumulation to ensure dispersion of said heavy hydrocarbon in water, and (2) at least once injecting water into said wellbore, contacting said preconditioned accumulation with said injected water and dispersing said preconditioned accumulation in said injected water.

5. The process described in claim 4 wherein steps (1) and (2) are repeated periodically.

6. The process described in claim 4- wherein the liquid mixture comprises solvent for hydrocarbons and an amount of surfactant at least 0.1 percent by weight of said liquid mixture.

7. The process described in claim 4 wherein the liquid mixture comprises solvent for hydrocarbons and an amount of surfactant at least 0.1 percent by weight of said liquid mixture and said injected water contains lyophilichydrophilic surfactant consisting essentially of an oxyethylene ether of an alkyl aryl compound in which the lyophilic portion has 9 to 18 carbon atoms and the hydrophilic portion has between 20 and mols of ethylene oxide in amount at least 0.1 percent by weight of the mixture of water and surfactant.

8. The process described in claim 4 wherein steps (1) and (2) are repeated alternately.

9. The process described in claim 4 wherein the injected water contains lyophilichydrophilic surfactant consisting essentially of an oxyethylene ether of an alkyl aryl compound in which the lyophilic portion has 9 to 18 carbon atoms and the hydrophilic portion has between 20 and 50 mols of ethylene oxide and wherein the volume of injected Water and the aforesaid surfactant is at least as great as the volume of the liquid mixture.

It). The process described in claim 4 wherein the volume of the liquid mixture is at least one-half the volume of said accumulation of heavy hydrocarbon, wherein the injected water contains lyophilic-hydrophilic surfactant consisting essentially of an oxyethylene ether of nonylphenol wherein the oxyethylene chain contains on the average 30 mols of ethylene oxide, and wherein the vol ume of injected water and surfactant is at least one-half the volume of said accumulation.

11. The process described in claim 4 wherein after dispersing said preconditioned accumulation in said injected water at least once daily a solvent is injected into the wellbore.

12. The process described in claim 4 wherein after dispersing said preconditioned accumulation in said injected Water at least once daily a lyophilic-hydrophilic surfactant consisting essentially of an oxyethylene ether of nonylphenol wherein the oxyethylene chain contains on the average 30 mols of ethylene oxide in a carrier liquid selected from the group consisting of (1) water, (2) oil, and (3) a mixture of oil and water is injected into the wellbore.

References Cited by the Examiner UNITED STATES PATENTS 2,050,931 8/1936 De Groote 2528.5 2,699,832 1/1955 Allen 16644 X 2,927,078 3/1960 Nathan 2528.55 2,978,026 4/1961 Bemis 166-44 2,998,066 8/1961 Nixon 166-41 FOREIGN PATENTS 778,819 7/1957 Great Britain.

CHARLES E. OCONNELL, Primary Examiner. BENJAMIN HERSH, Examiner. 

4. A PROCESS FOR TREATING A WELLBORE CONTAINING AN ACCUMULATION OF HEAVY HYDROCARBON WITHIN PASSAGEWAYS IN SAID WELLBORE TO CLEAN SAID PASSAGEWAYS OF SAID ACCUMULATION COMPRISING THE STEPS OF (1) CONTACTING AT LEAST ONCE IN AN ESSENTIALLY STATIC MANNER FOR AT LEAST 0.5 HOUR SAID ACCUMULATION WITH A LIQUID MIXTURE CONSISTING ESSENTIALLY OF SOLVENT FOR HYDROCARBONS AND LYOPHILIC-HYDROPHILIC SURFACTANT CONSISTING ESSENTIALLY OF AN OXYETHYLENE ETHER OF AN ALKYL ARYL COMPOUND IN WHICH THE LYOPHILIC PORTION HAS 9 TO 18 CARBON ATOMS AND THE HYDROPHILIC PORTION HAS BETWEEN 20 AND 50 MOLS OF ETHYLENE OXIDE, SAID LIQUID MIXTURE BEING CAPABLE OF PENETRATING AND SOFTENING THE AFORESAID ACCUMULATION TO PRECONDITION THE AFORESAID ACCUMULATION TO ENSURE DISPERSION OF SAID HEAVY HYDROCARBON IN WATER, AND (2) AT LEAST ONCE INJECTING WATER INTO SAID WELLBORE, CONTACTING SAID PRECONDITIONED ACCUMULATION WITH SAID INJECTED WATER AND DISPERSING SAID PRECONDITIONED ACCUMULATION IN SAID INJECTED WATER. 